1. Field of the Invention
The present invention relates to a power converter in a switching mode, and more specifically relates to a switching controller with switching frequency hopping.
2. Description of Related Art
Power converters have been used to convert an AC power source to a regulated voltage or current. The power converters need to maintain an output voltage, output a current, or output power within a regulated range for efficient and safe operation of an electronic device. A problem of utilizing pulse width modulation is that the power converters operate at a relatively high frequency compared to the frequency of the AC power source, which results in a high frequency signal generated by the power converters. Although the switching technique reduces the size of the power supply, switching devices generate electric and magnetic interference (EMI) which interferes with the power source. Generally, an EMI filter disposed at an input of the power supply is utilized to reduce the EMI. However, the EMI filter causes power consumption and increases the cost and the size of the power supply. In recent development, it has been proposed in related art to reduce the EMI by using frequency modulation or frequency hopping, e.g., in “Effects of Switching Frequency Modulation on EMI Performance of a Converter Using Spread Spectrum Approach” by M. Rahkala, T. Suntio, K. Kalliomaki, APEC 2002 (Applied Power Electronics Conference and Exposition, 2002), 17-Annual, IEEE, Volume 1, 10-14 Mar. 2002.